Just was wondering what effect changing airbleeds on holley dp750w/mech.
sec.would help street perf. Have BB402, th400, performance cam w/ported,stock heads that have the valves unshrouded,2.06 & 1.72.
I am thinking about installing holley main body conversion to HP style
which give me more adjustability. Good or bad.
Thanks, Joe

Unless you have hooked up a wide band a/f guage there is no good way to answer your question. "IF" your current fuel curve doesn't match your engines needs, then adding in more adjustability can lead to better results. If you were starting from scratch I might have suggested a Q-jet carb for smooth street performance.

Thomas

Changing air bleeds is somewhat like changing fuel jets in the carb which is not exactly a hop-up method. A tuning method yes, and tuning can result in more power true.

The rub with an air bleed is that it affects more than just air/fuel ratio, it also affects the timing of the fuel circuit. And to complicate things even more it affects the fuel curve which requires a whole additional explanation.

In an ideal carb, as more air flowed you would get an exact proportional additional amount of fuel. Problem is that vacuum across the venturis does not follow this nice clean linear relationship. As air flow increases a bit vacuum increases a lot. So the air bleed attempts to flatten or equalize this relationship by bleeding off some of the vacuum.

Thus the AFR is an interplay between fuel jet size, air bleed size, venturi design, booster venturi design, and engine air intake.

Actually for street driving you also have to factor in the interplay between different fuel circuits (idle and main) with somewhat different operational models too (the idle circuit is driven by engine vacuum rather than venturi vacuum).

A wide band O2 sensor can help greatly in tuning and getting all the parts to play nicely together. Any kind of in depth tuning of this nature requires careful testing and accurate records to track changes.

The Air Bleeds Change Things pretty fast, so you need to be real careful and have a wideband for the Hi Speed bleeds.

I just changed my Idol Air bleeds, went up, to lean my cruise mixture out. Now i have Nice clean plugs and WAY better MPG.

You shouldn't really have to cahnge the Hi speeds anyways IMO, not that much to be found with them unless you can really devote some time, and even then not much.

You shouldn't really have to cahnge the Hi speeds anyways IMO, not that much to be found with them unless you can really devote some time, and even then not much.
If you change the idle circuit air bleeds you may have to change the main circuit air bleeds to correlate. For example reducing idle air bleed size will cause more overlap between idle and main circuit operation. Enlarging main air bleed may be needed to correct.

I have considered reducing main air bleed sizes in both my primary and secondary barrels as a way to get more fuel in... I am already very close to the maximum jet size and need more.